KR101247906B1 - Ferritic stainless steel sheet for egr coolers - Google Patents

Abstract

[식 2]

[식 3]

In mass%, C: 0.03% or less, N: 0.05% or less, Si: 0.1% or more, 1% or less, Mn: 0.02% or more, 2% or less, Cu: 0.2% or more, 1.5% or less, Cr: 15% 25% or less, Nb: 8 (C + N)%-1% or less, Al: 0.5% or less at least, The remainder consists of Fe and an unavoidable impurity, In mass%, It is a following formula with respect to Ti A ferritic stainless steel sheet for an EGR cooler, which is set in a range satisfying 1 and 2 and contained in a range satisfying the following formula 3 with respect to C and Cu.
[Formula 1]

[Formula 2]

[Equation 3]

Description

Ferritic stainless steel sheet for EVR cooler {FERRITIC STAINLESS STEEL SHEET FOR EGR COOLERS}

The present invention relates to an EGR cooler for cooling exhaust gas with engine coolant, air, or the like in an exhaust gas recirculation (hereinafter referred to as EGR) system used in, for example, a diesel engine or a gasoline engine of an automobile. A ferritic stainless steel sheet for an EGR cooler suitable for use.

In recent years, in the automobile field, from the heightened awareness of environmental issues, exhaust gas regulations have been tightened, and measures for suppressing carbon dioxide emission have been advanced. In addition to the response from fuel surfaces such as bioethanol and biodiesel fuel, it is possible to improve the fuel efficiency by installing a heat exchanger that reduces weight and heat recovery of exhaust heat, or improves EGR, Diesel Particulate Filter (DPF), or Urea SCR (Selective Catalytic Reduction). Countermeasures such as providing an exhaust gas treatment device such as a system are carried out.

Among these, the EGR system aims to lower the combustion temperature and lower NOx, which is a noxious gas, by cooling the exhaust gas of the engine and then returning it to the intake side and reburning it. Moreover, the EGR cooler is an apparatus which cools exhaust gas with engine cooling water or air, and the heat exchange part requires favorable thermal efficiency, and it is desired that thermal conductivity is favorable.

Conventionally, an austenitic stainless steel such as SUS304, SUS316, or the like is generally used for an EGR cooler as disclosed in Patent Document 1, Patent Document 2, and the like below. However, in recent years, in order to further reduce NOx, there is a demand for lowering the exit temperature of the EGR cooler. In such austenitic stainless steels, there is a concern that thermal fatigue characteristics deteriorate due to the expansion of the temperature difference on the inlet and outlet sides. Therefore, attention is paid to ferritic stainless steel having superior thermal conductivity, smaller thermal expansion coefficient, and inexpensive than austenitic stainless steel.

In addition, although EGR coolers have been generally installed in diesel engines so far, their application to gasoline engines has also been considered in order to achieve both fuel efficiency improvement and NOx reduction by direct division. In general, gasoline engines are said to have a higher exhaust gas temperature than diesel engines, and the inlet side temperature of the EGR cooler reaches 500 to 600 ° C. This temperature range is an area where grain boundary corrosion due to sensitization is a concern in austenitic stainless steels such as SUS304, SUS316, and the like, and ferrite stainless steels are drawing attention from this point.

In the manufacture of an EGR cooler, especially its heat exchange part, it is common to assemble by brazing bonding. In addition, on the exhaust gas side of the EGR cooler, exhaust gas components can be condensed at the time of cooling. For this reason, brazing and corrosion resistance to exhaust gas condensate are required.

Patent Literature 3 below discloses a precoat lead coated metal sheet material which is prepared by suspending a Ni-based lead material together with an organic binder, followed by spray coating on a stainless steel sheet surface.

The following patent document 4 discloses the manufacturing method of the nickel lead coating stainless steel plate excellent in the magnetic brazing property which Ni-coated brazing material was coat | covered by the plasma spraying on the stainless steel plate which adjusted the surface roughness. In either case, the stainless steel that is the object of the examples is austenitic stainless steel.

In Patent Document 5 below, C: 0.5% or less, Si: 2% or less, Mn: 3% or less, S: 0.2% or less, Ni: 8-18%, Cr: 12-25%, and Mo: 0-4% , W: 0 to 2%, (Ni / Cu): 2 or more, and Nb: in the range of 0 to 2.5%, the exhaust gas recirculation component which consists of an austenitic stainless steel cast steel is disclosed.

In Patent Document 6, a fin is inserted into a pipe or between a plurality of pipes to form a high heat fluid passage, and in the heat exchanger in which a low heat fluid is formed adjacent to the high heat fluid, the fin is connected to an austenitic stainless steel and a pipe. A heat exchanger composed of ferritic stainless steel is disclosed, and SUS304 is used as austenitic stainless steel and SUS430 is used as ferritic stainless steel. It has a structure using the coefficient of thermal expansion difference of austenitic stainless steel and ferritic stainless steel, and can be manufactured at low cost and in a short time by eliminating brazing bonding. Therefore, while the technology regarding brazing property is not recognized, it does not mention the condensate corrosion resistance.

In Patent Document 7, an inner fin which is built into a flat tube embedded in an exhaust gas heat exchanger, divides a wide direction of an exhaust gas flow path formed by a flat tube into small compartments, and forms a plurality of elongated exhaust gas flow paths. An inner fin of an exhaust gas heat exchanger having a material of an inner fin of ferritic stainless steel is disclosed. The heat resistance was improved by setting it into the shape which considered the moldability of ferritic stainless steel, and SUS405 and SUS446 are illustrated. Only good heat resistance and bendability are listed as necessary characteristics, and no mention is made of brazing resistance or condensate corrosion resistance.

In Patent Document 8, C: 0.025% or less, Si: 0.10% or less, Mn: 1.0% or less, Cr: 17.0 to 25.0%, Ni: 0.50% or less, Mo: 0.50 to 2.00% or less, Al: 0.025% or less And N: 0.025% or less, and ferritic stainless steels for heat exchangers containing any one or two of Nb and Ti in a range of 10 (C + N) to 1.0% are disclosed. From the viewpoint of brazing properties, the amount of Si and Al is limited, and from the viewpoints of corrosion resistance and oxidation resistance, high Cr and Mo addition amounts are used. Among them, Mo is an element particularly effective in corrosion resistance to exhaust gas condensed water. When the corrosive environment becomes more severe, it is necessary to increase the Mo addition amount, but since Mo is an expensive element, there is a problem in that it is inferior in cost performance.

In following patent document 9, C: 0.08% or less, Si: 0.01-2.0%, Mn: 0.05-1.5%, P: 0.05% or less, S: 0.01% or less, Cr: 13-32%, Mo: 3.0% or less Disclosed is a ferritic stainless steel for ammonia-water absorption cycle heat exchanger having excellent solderability in a range of 0.005 to 0.1%, Ni: 1.0% or less, Cu: 1.0% or less, and Ti: 0.05% or less. Ti is limited to 0.05% or less from the viewpoint of solderability (brazing property), and Cr is made 13% or more from the viewpoint of corrosion resistance in a high temperature and high pressure ammonia water environment. Although Mo, Ni, and Cu are described as an effective element for corrosion resistance, they are not described about the required amount.

In following Patent Document 10, Cr: 18.0 to 27.0%, Cu: 0.8 to 3.5%, Si: 0.5 to 2.0%, Mo: 0.5 to 1.5%, Nb: 2.5% or less, Ni: 0.6% or less, C: 0.12% Mn: 1.0% or less, Al: 0.10% or less, P: 0.15% or less, S: 0.15% or less, N: 0.10% or less, and (Cu + Si) is more than 2.0%, and is excellent in acid resistance. Ferritic stainless steel castings are disclosed. The ferrite system is defined from the viewpoint of machinability, and the Cr, Cu, Si and (Cu + Si) amounts are defined from the viewpoint of acid resistance. Since a large amount of Cu and Si are required from a viewpoint of acid resistance, when it becomes hard and is used as a steel plate, there exists a problem in moldability.

Japanese Laid-Open Patent Publication No. 2007-64515 Japanese Laid-Open Patent Publication No. 2007-224786 Japanese Patent Laid-Open No. Hei 1-249294 Japanese Patent Application Laid-Open No. 2001-26855 Japanese Laid-Open Patent Publication No. 2003-193205 Japanese Laid-Open Patent Publication No. 2005-55153 Japanese Laid-Open Patent Publication No. 2008-96048 Japanese Patent Application Laid-Open No. 7-292446 Japanese Patent Laid-Open No. 11-236654 Japanese Laid-Open Patent Publication No. 2008-195985

The present invention has been proposed in view of such a conventional situation, and an object thereof is to provide a ferritic stainless steel sheet for an EGR cooler having excellent brazing properties and corrosion resistance to exhaust gas condensate.

The summary of this invention aimed at solving the said subject is as follows.

[1] at mass%

C: 0.03% or less,

N: 0.05% or less,

Si: 0.1% or more, 1% or less,

Mn: 0.02% or more, 2% or less,

Cu: 0.2% or more, 1.5% or less,

Cr: 15% or more, 25% or less,

Nb: 8 (C + N)% or more, 1% or less,

Al: 0.5% or less at least, the remainder being made of Fe and unavoidable impurities,

With respect to Ti, it is set as the range which satisfy | fills following formula 1 and 2,

It contains C and Cu in the range which satisfy | fills following Formula 3, The ferritic stainless steel plate for EGR coolers characterized by the above-mentioned.

[Formula 1]

[Formula 2]

[Equation 3]

[2] in mass%,

Mo: 3% or less,

Ni: It contains any 1 type, or 2 or more types of 3% or less, and also contains it in the range which satisfy | fills following formula 4, The ferritic stainless steel plate for EGR coolers as described in said [1] characterized by the above-mentioned.

[Formula 4]

[3] In addition, in mass%,

V: 3% or less,

W: The ferritic stainless steel sheet for EGR coolers as described in said [1] or [2] characterized by containing any one or both of 5% or less.

[4] In addition, in mass%,

Ca: 0.002% or less,

Mg: 0.002% or less,

B: The ferritic stainless steel sheet for an EGR cooler according to any one of the above [1] to [3], which contains any one or two or more of 0.005% or less.

[5] C + N: 0.015% or more, the ferritic stainless steel sheet for EGR cooler according to any one of the above [1] to [4].

As described above, according to the present invention, a ferritic stainless steel sheet having excellent brazing properties and corrosion resistance to exhaust gas condensate can be provided. It is possible to.

1 is a characteristic diagram showing the relationship between the wet diffusion of lead and the Ti and Al amounts.
Fig. 2 is a characteristic diagram showing the relationship (pH1.5) between the corrosion rate and Cr + 2.3Cu ≧ 18 in the exhaust gas simulated condensate.
Fig. 3 is a characteristic diagram showing the relationship (pH1.5) between the corrosion rate in the exhaust gas simulated condensate and Cr + 1.9 M + 1.6 Ni + 2.3 Cu.
4 is a characteristic diagram showing the influence (pH1) of Cu on the corrosion rate in the exhaust gas simulated condensate.
Fig. 5 is a characteristic diagram showing the influence (pH1) of Mo on the corrosion rate in the exhaust gas simulated condensate.
Fig. 6 is a characteristic diagram showing the effect of Ni (pH 0.5) on the corrosion rate in the exhaust gas simulated condensate.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings.

Brazing property by Ni and Cu is calculated | required for an EGR cooler. For this reason, the present inventors earnestly examined the influence of the alloying element on brazing property. As a result, as shown in the following formulas 1 and 2, in the ferritic stainless steel sheet, good brazing is applied to Ti, which is often added for the purpose of improving workability and grain boundary corrosion resistance, and Al added for the purpose of deoxidation. It was found that there was an upper limit to secure the sex.

[Formula 1]

[Formula 2]

In order to obtain good brazing property, molten lead needs to wet-diffuse on the surface of the stainless steel sheet, but the wettability affects the surface coating formed on the stainless steel sheet in the brazing atmosphere. In addition, in the brazing atmosphere, even if the oxides of Fe and Cr are maintained under reduced conditions, Ti and Al, which are more easily oxidized than Fe and Cr, form oxides, inhibit the wet diffusion of lead and deteriorate brazing properties. . Contributing to the formation of such a film is Ti and Al in solid solution, and when present as a relatively stable nitride even at a brazing temperature, it does not contribute to the formation of the film and does not inhibit the wet diffusion of lead.

From this point of view, the relationship between the Ti, Al amount and the wet diffusivity of lead was evaluated under the same test conditions as in the examples described later using 16-21 Cr ferritic stainless steel sheets shown in Table 1. In Table 1, the remainder is Fe and unavoidable impurities. The results are shown in Fig.

From the result shown in FIG. 1, it turned out that the wet diffusivity of lead is favorable in the range which satisfy | fills said Formulas 1 and 2. In addition, when the Ti to Al amount did not satisfy the above conditions, the surface coating after the brazing heat treatment was analyzed, whereby a thickened oxide film of Ti to Al was uniformly formed at a thickness of several tens to several hundred nm. Therefore, it is thought that such film formation inhibits the wet diffusion of lead.

In the EGR cooler which this invention aims at, strength is also needed and it is preferable that the intensity | strength fall after brazing is small. When brazing at high temperature, such as Ni brazing and Cu brazing, 1000-1150 degreeC, it is thought that it is important to suppress the strength fall accompanying grain coarsening. In order to suppress coarsening of a crystal grain, pinning by a precipitate is useful. In the present invention, it was found that by using Nb carbonitride as a precipitate and C + N being 0.015% or more, the precipitation amount and stability of Nb carbonitride, which is useful for suppressing coarsening of crystal grains, are ensured (Japanese Patent Application No. See, eg, 2007-339732.

In the EGR cooler, acidic condensed water consisting of sulfuric acid, nitric acid and organic acid is generated due to SOx, NOx and HC contained in the exhaust gas. In the EGR cooler, unlike downstream members such as mufflers, the acid concentration of the condensate produced is also high because the exhaust gas before the catalyst is located directly under the catalyst and is directly under the engine.

In recent years, with globalization, low-grade fuel having a high S concentration may be used as fuel for automobiles. In this case, the concentration of sulfuric acid in the condensed water also increases. Such an increase in acid concentration leads to a decrease in pH, and it is said that the pH of the condensed water of the EGR cooler reaches about 1.5. Generally, since the plate | board thickness of the heat exchange part of an EGR cooler is thin as 0.1-0.5 mm, excellent corrosion resistance is needed in the condensate of about pH1.5 which consists of such sulfuric acid, nitric acid, and an organic acid.

Therefore, the present inventors examined the effect of Cr and Cu on the condensate corrosion resistance by using the ferritic stainless steel of 16-19Cr and 0-0.5Cu by the corrosion test on the same conditions as an Example. The result is shown in FIG. In addition, NO ^{3 -} ions, it functions as a corrosion-inhibiting ion species, and by no additives was to evaluate the safety side.

Although the test result in the solution of pH1.5 is shown in FIG. 2, it turns out that it is excellent in corrosion resistance by satisfying Cr + 2.3Cu≥18.

Next, Ni, Mo were added, and ferrite stainless steels in the range of 13 to 21 Cr, 0 to 2 Mo, 0 to 3 Ni, and 0 to 1 Cu were used to effect the effects of Cr, Ni, Mo, and Cu on the condensate corrosion resistance. It examined by the corrosion test on the same conditions as an example. The result is shown in FIG. In addition, NO ^{3 -} ions were also added without addition.

Although the test result in the solution of pH1.5 is shown in FIG. 3, although any element among Cr, Ni, Mo, and Cu is effective for improving corrosion resistance, Cu is the most effective for improving corrosion resistance, and Cr + 1.9Mo + 1.6Ni + 2 It can be seen that excellent corrosion resistance is achieved by satisfying .3Cu?

Here, the coefficient of each alloying element calculates the contribution of the alloying element with respect to a critical pH by multiple regression analysis. In addition, the critical pH is the upper limit pH at which the corrosion rate becomes 0.1 g · m ⁻² · h ⁻¹ or less. 4 shows the effect of Cu on the corrosion rate in the solution at pH1, FIG. 5 shows the effect of Mo on the corrosion rate in the solution at pH1, and FIG. The effect of Ni on the corrosion rate in each is shown.

4, 5, and 6 show that the corrosion rate of Cu is considerably lowered with a smaller addition amount than that of Mo and Ni, and is a very effective element for improving the corrosion resistance. Moreover, although Cu is known as an element which improves acid resistance, when the influence of Cu was examined by electrochemical measurement, the phenomenon that corrosion potential is inactivated by Cu addition was recognized. This indicates that Cu has a function of promoting passivation in addition to the active dissolution inhibiting action, and it is considered that the contribution to improvement of corrosion resistance has been increased by these two effects.

This invention is made | formed based on the said knowledge, Comprising: It provides the ferritic stainless steel plate for EGR coolers which has the outstanding brazing property and corrosion resistance with respect to exhaust gas condensate, The summary is made as the content of a claim. to be.

Hereinafter, the reason which limited each composition of the ferritic stainless steel plate for EGR coolers is demonstrated. In addition, in the following description, unless otherwise indicated,% of each component shall represent the mass%.

(C: 0.03% or less)

Since C reduces intergranular corrosion resistance and workability, it is necessary to suppress the content low. For this purpose, C was made into 0.03% or less. However, excessively lowering the grain coarsening at the time of brazing and increasing the refining cost, it is preferable to make C 0.002% or more. More preferably, it is 0.005 to 0.025%.

(N: 0.05% or less)

Although N is an element useful for pitting resistance, since it reduces intergranular corrosion resistance and workability, it is necessary to suppress the content low. For this purpose, N was made into 0.05% or less. However, excessively lowering promotes grain coarsening at the time of brazing and raises the refining cost. Therefore, it is preferable to make N 0.002% or more. More preferably, it is 0.005 to 0.03%.

(Si: 0.1% or more, 1% or less)

Si is required as a deoxidation element because it restricts Ti and Al useful as a deoxidation element. In addition, since the Cr concentration of the surface is lowered by the brazing heat treatment, Si is an effective element for improving the oxidation resistance after brazing. For this purpose, it is necessary to contain Si at least 0.1% or more. However, since excessive addition reduces workability, it is preferable to set it as 1% or less. More preferably, it is 0.1 to 0.5%.

(Mn: 0.02% or more, 2% or less)

Mn is an element useful as a deoxidation element and needs at least 0.02% or more. However, when it contains excessively, since corrosion resistance deteriorates, it is preferable to set it as 2% or less. More preferably, it is 0.1 to 1%.

(Cu: 0.2% or more, 1.5% or less)

Cu is an important element similar to Cr in securing the exhaust gas condensate water corrosion resistance, and it is required at least 0.2% or more. On the other hand, although Cu can improve corrosion resistance as the content is increased, since excessive addition degrades workability, it is preferable to set it as 1.5% or less. More preferably, it is 0.2 to 1.0%.

(Cr: 15% or more, 25% or less)

Cr is an element which is a basic element in securing exhaust gas condensate corrosion resistance and oxidation resistance and is required at least 15% or more. On the other hand, although Cr can improve corrosion resistance and oxidation resistance as the content increases, since excess addition reduces workability and manufacturability, it is preferable to set it as 25% or less. More preferably, it is 17 to 23%.

(Nb: 8 (C + N)% or more, 1% or less)

Since Nb is an element which is useful in fixing C and N and improving intergranular corrosion resistance of a weld part, Nb needs to contain 8 times or more of (C + N) amount. In addition, Nb is also useful for improving the high temperature strength and is required for a member to be used at a high temperature such as an EGR cooler. Moreover, Nb carbonitride is useful for suppressing grain coarsening at the time of brazing. However, since excessive addition reduces workability and manufacturability, it is preferable to set it as 1.0% or less. More preferably, it is 10 (C + N)-0.6%.

(C + N: 0.015% or more)

Moreover, it is preferable to make C + N 0.015% or more from a viewpoint of suppressing the strength fall accompanying crystal grain coarsening at the time of brazing. C + N becomes like this. Preferably it is 0.02% or more. Since excessive addition of C and N reduces intergranular corrosion resistance and workability, it is preferable to make C + N 0.04% or less.

(Al: 0.5% or less)

Al is an element useful for refining because it has a deoxidizing effect and the like, and has an effect of improving moldability. However, Al is 0.5% or less because it inhibits brazing property, which is the most important characteristic of the present invention. Preferably it is 0.001 to 0.1%, More preferably, it is 0.001 to 0.05%.

(Ti: range satisfying Expressions 1 and 2)

In the present invention, in the brazing property which is the most important characteristic, it is necessary to satisfy the above formulas 1 and 2 at the same time in order to obtain good wet diffusion of lead. In order to satisfy this, Ti was made into the range which satisfy | fills said Formula 1 and 2 based on the said knowledge. The value of Ti-3N is preferably 0.02% or less. However, if the content of Ti is too low, the workability is deteriorated. Therefore, it is preferable to adjust the content of Ti so that the value of Ti-3N is -0.08% or more. If workability or the like is not particularly required, Ti may not be added.

(Cr, Cu: range satisfying Expression 3)

In this invention, in order to express favorable corrosion resistance in the exhaust gas condensate of pH 1.5 which consists of sulfuric acid, nitric acid, and an organic acid, it is necessary to satisfy following formula (3) about Cr and Cu.

[Equation 3]

In addition, in this invention, you may further contain either or both of Mo and Ni.

(Mo: 3% or less)

Mo can be contained 3% or less as needed in improving corrosion resistance. It is 0.3% or more that a stable effect is obtained. However, excessive addition deteriorates workability and is expensive, leading to an increase in cost. Therefore, it is preferable to contain 0.3 to 3%.

(Ni: 3% or less)

Ni can be made to contain 3% or less as needed in order to improve corrosion resistance. It is 0.2% or more that a stable effect is obtained. However, excessive addition deteriorates workability and is expensive, leading to an increase in cost. Therefore, it is preferable to contain 0.2 to 3%.

In addition, when either or both of Mo and Ni are added, it is necessary to satisfy the following formula 4 in order to express good corrosion resistance in the exhaust gas condensate at a pH of about 1.5 consisting of sulfuric acid, nitric acid and organic acid.

[Formula 4]

In the present invention, one or both of V and W may be further contained.

(V: 3% or less)

In improving the corrosion resistance, V can be contained 3% or less as necessary. It is 0.2% or more that a stable effect is obtained. However, excessive addition deteriorates workability and is expensive, leading to an increase in cost. Therefore, it is preferable to contain 0.2 to 3%.

(W: 5% or less)

W can be made to contain 3% or less as needed in order to improve corrosion resistance. It is 0.5% or more that a stable effect is obtained. However, excessive addition deteriorates workability and is expensive, leading to an increase in cost. Therefore, it is preferable to contain 0.5 to 5%.

In the present invention, any one or both of Ca, Mg, and B may be further contained.

(Ca: 0.002% or less)

Since Ca has a deoxidation effect etc., it is an element useful for refinement | purification, and can be contained 0.002% or less as needed. In addition, when it contains Ca, it is preferable to set it as 0.0002% or more from which a stable effect is acquired.

(Mg: 0.002% or less)

Since Mg has a deoxidation effect etc., it is an element useful for refinement | purification, and can be contained 0.002% or less as needed from what is useful also for refine | miniaturizing a structure and improving workability and toughness. In addition, when it contains Mg, it is preferable to set it as 0.0002% or more from which a stable effect is acquired.

(B: 0.005% or less)

B is an element useful for improving secondary workability and can be contained 0.005% or less as necessary. In addition, when it contains B, it is preferable to set it as 0.0002% or more from which a stable effect is acquired.

Moreover, it is preferable to set it as 0.04% or less from a viewpoint of weldability among the unavoidable impurities. In addition, about S, it is preferable to set it as 0.01% or less from a corrosion resistance viewpoint.

The manufacturing method of the stainless steel of this invention should just be a general process which manufactures a ferritic stainless steel. Generally, molten steel is used by converter or electric furnace, refined by AOD furnace or VOD furnace, etc., and then steel pieces are formed by continuous casting method or ingot method, and then hot rolling-pickling-hot rolling-finishing-annealing-pickling It is manufactured through the process of. If necessary, annealing of the hot rolled sheet may be omitted, or cold rolling-finishing annealing-pickling may be performed repeatedly.

(Example)

Hereinafter, the effects of the present invention will be more obvious by Examples. In addition, this invention is not limited to a following example, It can change and implement suitably in the range which does not change the summary.

In this embodiment, a steel having a chemical composition shown in Table 2 is prepared, and a cold rolled steel sheet having a sheet thickness of 0.4 mm is produced through a hot rolling, cold rolling, and annealing process, and the brazing properties and corrosion resistance in the simulated condensate of the exhaust gas are evaluated. It was.

(Brazing)

After the 50-mm width and 70-mm length test piece was cut out from the cold rolled steel plate, wet polishing was performed to # 400 by one side with emery paper. Thereafter, 0.1 g of Ni lead was placed on the polished surface and heated at 1100 ° C. in a vacuum atmosphere of 5 × 10 ⁻³ torr for 10 minutes. And after cooling to normal temperature, the lead area after heating was measured. The measurement results are shown in Table 3.

In addition, about the brazing property shown in Table 3, when the lead area after heating is 2 times or more with respect to the lead area before heating, when wet diffusion is less than 2 times, wet diffusion is "Bad (bad) Was evaluated. Moreover, the cross-sectional microstructure was observed after that. And microstructure is "Good (good)" by measuring the number of crystal grains which exist in a plate | board thickness direction over the range of 20 mm in length in parallel in a rolling direction, and having two or more crystal grains in a plate | board thickness direction. The microstructure evaluated as "Bad (bad)" that only one exists.

(Corrosion test)

A 25 W × 40 L test piece was cut from the cold rolled steel sheet, and the entire surface was wet-polished to # 320 with emery paper. With ammonium chloride, sulfuric acid, formic acid, acetic acid as reagent, 50ppmCl ^- to prepare a solution of a _{^{- + 5000ppmSO 4 2 - + 5000ppmHCOO}} - + 3000ppmCH 3 COO. Then, it adjusted to pH1.5 and pH1.0 using sulfuric acid or ammonia water. The test piece was immersed in this solution heated to 60 degreeC for 3 h, and the corrosion rate was calculated | required from the mass change before and behind immersion. The measurement results are shown in Table 3.

In addition, about the corrosion test shown in Table 3, it is "Bad" that the corrosion rate is 0.1 g * m- ^{2 *} h- ¹ or less, and exceeding 0.1g * m- ^{2 *} h- ¹ "Bad. (Defect) "was evaluated.

From the test results shown in Table 3, Experimental Example No. within the scope of the present invention. Steels 1 to 13 have good wet diffusion property of lead, suppressed grain coarsening after brazing, and good corrosion resistance in exhaust gas simulated condensed water at pH 1.5. Among these, Experimental Example No. Steels of 2, 3, 4, 6, 7, 9, 10, and 11 exhibit good corrosion resistance in the exhaust gas simulated condensate at pH 1.0, and can be used for EGR cooler materials that can cope with a more severe corrosive environment. Suitable as.

On the other hand, Experimental Example No. in which Al deviates from the scope of the present invention. 14, Experimental Example No. 2 that does not satisfy the above formula 2. It turns out that 15 is inferior in the wet diffusion property of lead. In addition, all of the said Formulas 1-3 are Experimental example No. which departs from the scope of the present invention. It can be seen that 16 is inferior in both the wet diffusion property of lead and the corrosion resistance in the exhaust gas simulated condensate. In addition, the amount of Cr and said Formula 3 are out of the range of this invention, and (C + N) amount is less than 0.015% of the experiment example. 17 shows that corrosion resistance in the exhaust gas simulated condensed water is inferior and coarsening of crystal grains is remarkable.

The ferritic stainless steel sheet having excellent brazing properties and corrosion resistance to exhaust gas condensate of the present invention is suitable as an EGR cooler member, and especially a heat exchange member of an EGR cooler. In addition, it is also suitable as an exhaust gas path member exposed to exhaust gas condensed water and brazed.

Claims (5)

In mass%,
C: more than 0% and 0.03% or less,
N: more than 0%, 0.05% or less,
Si: 0.1% or more, 1% or less,
Mn: 0.02% or more, 2% or less,
Cu: 0.2% or more, 1.5% or less,
Cr: 15% or more, 25% or less,
Nb: 8 (C + N)% or more, 1% or less,
Al: 0% or more and 0.5% or less at least, the remainder being made of Fe and inevitable impurities,
In mass%,
With respect to Ti, it is set as the range which satisfy | fills following formula 1 and 2,
A ferritic stainless steel sheet for EGR cooler, characterized by containing Cr and Cu in a range satisfying the following formula (3).
[Formula 1]

[Formula 2]

[Equation 3]

The method according to claim 1, wherein in mass%,
Mo: more than 0% and 3% or less,
Ni: The ferritic stainless steel sheet for EGR coolers, which further contains any one or both of more than 0% and 3% or less and further satisfies the following formula (4).
[Formula 4]

The mass% according to claim 1 or 2,
V: more than 0%, 3% or less,
W: more than 0%, 5% or less,
Ca: greater than 0% and 0.002% or less,
Mg: more than 0% and 0.002% or less,
B: The ferritic stainless steel sheet for an EGR cooler, further containing at least one of more than 0% and 0.005% or less. C + N: 0.015% or more and 0.04% or less, The ferritic stainless steel plate for EGR coolers of Claim 1 or 2 characterized by the above-mentioned. C + N: 0.015% or more and 0.04% or less, The ferritic stainless steel plate for EGR coolers of Claim 3 characterized by the above-mentioned.

Images